Inkless printing of labels is an alternative to traditional label printing techniques such as inkjet or thermal transfer where a pigment is applied to a label substrate. The inkless method utilises a substrate whose physical properties (in particular its colour) can be altered upon irradiation with patterns of radiation.
Label application methods and apparatus are well known in the packaging industry. Typically, many label application methods operate using pre-cut labels supported on a backing liner. Each label may be printed with an identical design or may have regions printed with variable information. The labels and backing liner are rewound after printing onto a reel. The reel can be fitted to a label applicator so as to draw forward a continuous strip of liner and labels. The labels are then separated from the liner and applied to an object (typically a package, case, box, carton or product). One example of such labels is marketed by Macsa id wherein pre-cut labels are provided on a backing liner and a CO2 laser is used to form an image on the labels.
The above techniques all have the disadvantages the backing liner is waste and needs to be disposed of or recycled. Additionally, the backing liner adds thickness, which limits the number of labels that can be provided on a reel for use in a labelling apparatus. Furthermore, use of pre-cut labels requires an additional level of complexity in manufacturing since the labels must be cut after formation on the backing liner.
In view of the above issues, efforts have been made to develop linerless labels. In order to apply individual labels printed on a continuous strip of label substrate to a succession of objects, it is necessary to cut the label substrate. One well known technique is to use a mechanical blade to cut the substrate. This has the disadvantage that the blade wears over extended use and must be replaced. Additionally, the blade accumulates debris and adhesive during use and thus requires regular cleaning.
In order to avoid the use of mechanical blades attempts have been made to provide preformed perforations into label substrate. With this approach, it is not possible to adjust the length of label at the point of application even if the size of the imaged region can be modified by the printing or imaging system. Moreover, variation in tension applied to the label substrate (or indeed variations in the perforations) can cause premature tearing of the perforations, particularly when the strip of label substrate is rewound during the manufacturing process. It is therefore necessary to implement the rewind process at a significantly lower tension than normal which leads to a larger diameter reel for a given length of label substrate. Typically, the reduction in tension during rewind leads to a reel diameter that is not significantly smaller than a reel of labels on a backing liner. Therefore any benefit of removing a liner from the label with regard to increasing in the interval to reload the machine is lost.
In our co-pending UK patent application No. 1506312.6 (and family), a linerless label printing method and apparatus is disclosed using laser illumination means both for imaging and for cutting of individual labels at the correct location. To minimise cost, it is preferable to use a single laser illumination means to both image and cut the labels cutting and imaging operation being distinguished by varying the power output of the laser illumination means and the scan speed of the laser spot. Typically, imaging operation might be carried out at say 25% of maximum power output with a scan speed of 6000 mm/s whilst cutting operation may require 100% power output with a scan speed reduced to 300 mm/s. One of the problems with using the same laser illumination means for marking and cutting is that the spot size optimised for marking is not optimum for cutting. Typically, with the key limitation upon speed of imaging being provided by the difficulties in increasing scan speed, a larger spot size is favoured for imaging. Nevertheless, the optimum spot size for writing text may be different to the optimum spot required for imaging large linear bar codes.
The larger spot size required for marking means that when the laser needs to cut the time required for this operation is longer, increasing costs. Additionally, the kerf cut width is wider than is desirable, potentially increasing the impact on the fume extraction system and thereby limiting filter lifetime in said extraction system.
Even with a relatively large spot size for imaging, large linear bar codes may require between 1 and 6 scans per dark bar. Requiring multiple scans limits the maximum imaging rate of the label. Whilst this can be addressed by increasing the spot size further, this would have an even more significant impact on the cutting operation.
It is therefore an object of the present invention to provide an improved method and apparatus for printing and cutting labels that at least partially overcomes or alleviates the above problems.